With the development of the microfabrication of a semiconductor integrated circuit, the exposure light wavelength of a photolithography equipment has been shortened from a g-line to an i-line, and furthermore, an excimer laser. However, a requirement for the microfabrication has been given earlier than a progress in a reduction in the wavelength of the equipment, and in recent years, it has been necessary to reduce a pattern dimension to be equal to or smaller than a wavelength. When the pattern dimension is equal to or smaller than the wavelength, a pattern cannot be formed faithfully to a layout in a complicated pattern which is connected like a key, causing the symmetry of a memory cell to be broken. However, it has conventionally been necessary to bend the shape of a diffusion layer like a key in order to cause a p-well region to come in contact with a substrate. Consequently, the symmetry has been deteriorated, resulting in a hindrance to the microfabrication. In order to eliminate the drawback, there has been known a technique in which a p-well region having an inverter constituting an SRAM formed therein is divided into two portions, the portions are provided on both ends of an n-well region, a diffusion layer forming a transistor is not bent, and the direction of an arrangement is set to be parallel with a well region or a bit line so that the diffusion layer is prevented from taking a complicated shape, resulting in easy microfabrication (see JP-A-2001-28401 Publication (FIG. 1), for example).
Moreover, a CAM has been known as a memory to be used in an LSI for a router which carries out the relay of a packet and the selection of a route between different network addresses in the Internet communication network. As an example of such a CAM, there has been known a memory of a ternary type in which the 2-bit information of a data comparison mask is stored in a memory cell and the result of a comparison with input data is output to a match line (see U.S. Pat. No. 6,154,384 specification, for example).